The Romans built a large network of roads in Britain. These roads, as in other parts of the Empire, were very important in maintaining both its stability and expansion.
The roads were built to a standard pattern that ensured they were sturdy and stable - able to withstand the pounding of the feet of the centurions that used them.
When building for military use, the roads were typically built as straight as possible to connect the garrisons and towns, sometimes resulting in grades that were impractical for mercantile use. Civil routes tended more to follow the contours of the land in order to link farms and estates to their markets - thereby ensuring more manageable grades that carts and wagons could deal with.
I can imagine the military engineers sitting in a dark, smoke-filled tent, laying out the route for their roads. There is a hill in the way, no problem, we'll go straight over it, our soliders can handle it. There is already a road there, doesn't matter, we need a new one. Once they came up with a plan (sometimes this took much longer than you might have expected), they presented it to the community for feedback (as the farmers wold use the road as well). The community's thoughts on brick colour, flower planting, etc would have been listened to closely.
The civil engineers on the other hand, would have met in bright sunny open town squares to do their designing. They talked to the townspeople about what features (e.g. maximum grade, curbs, extra width, etc) were needed for the road and where it would be best laid out. Only after this did they then look at the map and work out how to meet this requirements given the restrictions of the terrain and map. If there were existing roads that could be leveraged, do so. Why build another?
I don't really believe either of these two extremes happened (or happens) but the analogy just seemed to perfect to pass up. :-)